A generic proportional or adjusting magnet of the pre-cited type is known from DE-OS 22 55 272. This adjusting magnet essentially comprises a hollow cylindrical coil spool and a coil winding arranged thereon. The coil spool and the coil winding are collectively enclosed circumferentially by a hollow cylindrical magnet housing. The coil spool is limited at its ends by two axially spaced pole shoes, one of which pole shoes is structurally integral with the magnet housing. The adjusting magnet further comprises an axially moveable cylindrical armature which is arranged in the hollow cylinder of the coil spool that is configured as an armature space. The electromagnetically produced axial movements of the armature are transmitted against the force of a compression spring to a hydraulic valve piston via a push rod connected to the armature. The armature is mounted for low friction in rotary, longitudinally moveable axial guides so that a uniform air gap is formed between the outer peripheral surface of the armature and the coil spool, and the radial forces acting on the armature, which increase considerably with an increasing eccentricity of the armature, are reduced to a minimum. The rotary, longitudinally moveable axial guides are configured as two axial ball bearings which are pressed into the pole shoes of the adjusting magnet. The ends of the push rod, which has an extension on one side and which extends axially through the armature, are mounted in these ball bearings. In the interior of each axial ball bearing, there is arranged an axially moveable ball cage with a number of circumferentially uniformly spaced balls whose inner running track is formed by the outer peripheral surface of the push rod, while the outer running track is formed by the inner peripheral surfaces of the two bearing bushings. The armature is mounted in these axial ball bearings for axial movements between the pole shoes, and, for avoiding a seating of the armature on the pole shoes and the concomitant sudden increase of axial force on the armature, so-called anti-stick discs of a non-ferromagnetic material are arranged on the ends of the armature.
A drawback of this prior art adjusting magnet is that, although the axial ball bearings for the rotary, longitudinal axial guidance of the armature have very good friction properties, their complicated structure consisting of bearing bushing, ball cage and balls is relatively cost-intensive, and their assembly is thus likewise complicated and expensive, so that the total manufacturing costs of an adjusting magnet of this type are unreasonably high. Moreover, the wall thicknesses of the bearing bushings of such axial ball bearings, which are generally made by deep drawing, are inherently non-uniform due to the peculiarities of their shaping process and this results in a non-concentricity of their inner peripheral surfaces so that it is only rarely possible to achieve the desired exact, centered mounting of the armature, and undesired radial forces acting on armature cannot be eliminated.